Method of manufacturing a dental crown

ABSTRACT

The method of manufacturing a dental crown includes the steps of making an impression of the patient&#39;s teeth including the tooth to be crowned and then making a first model from the impression. The tooth to be crowned is then treated by removing surface portions to provide a prepared tooth. An impression is made of the patient&#39;s teeth with the prepared tooth and from this impression a second model is made. By use of heat and pressure a thin acrylic releasing plastic foil is applied over the second model. By use of heat and pressure a thicker plastic foil form is made from the first model. Moldable crown formed material is then placed on the plastic foil encapsulated prepared tooth on the second model. The plastic foil form is then placed over the foil covered second mold to shape the moldable crown forming material. The crown forming material is then hardened to create a crown that is removed from off of the foil covered second model and out of the plastic foil form. The created crown is then further hardened and polished as necessary and cemented onto the patient&#39;s prepared tooth.

REFERENCE TO PENDING APPLICATIONS

This application is not related to any pending applications.

REFERENCE TO MICROFICHE APPENDIX

This application is not referenced in any microfiche appendix.

BACKGROUND OF THE INVENTION

For many years dentistry has enhanced the quality of life of mankind byproviding crowns for damaged, decayed or disfigured teeth. When a toothis partially broken off, is disfigured caused by discoloration or hasbeen damaged by decay, a modern dentist can restore the tooth both infunction and appearance to a desired external shape by applying a crown.As commonly practiced today, a dentist first takes an impressionemploying a plastic material of the patient's teeth, typically animpression will include all of the patient's upper teeth or all of thepatient's lower teeth. From such impression a mold is easily made byfilling the impression with plaster that hardens and, after hardening,is easily removable from the soft plastic mold to faithfully replicate apatient's upper or lower teeth, including the adjacent gum areas. Thedentist then prepares the damaged tooth to receive a crown by removingexternal portions, that is by grinding away external parts to reduce thetotal dimensional size of the tooth to be crowned so that all exteriorportions thereof are confined within an area less than that of thedesired crown. After the tooth has been prepared by removing exteriorportions, a second impression is taken from which a second plaster moldis made.

These plaster molds are then sent off to a dental laboratory where alaboratory technician can manufacture a crown. After the crown iscompleted it is returned to the dentist who then cements it in place onthe patient's prepared tooth.

This procedure works satisfactorily except that it takes several days upto several weeks from the time the dentist makes the impressions untilthe crown is returned to the dentist for installation in the patient'smouth. Typically when a tooth is prepared to receive a crown it is veryvisually distractive. To enable a patient to function both physically,that is to masticate food, and to function socially, that is to have areasonable appearance, the typical procedure is that the dentist forms atemporary crown by molding temporary crown forming material on theprepared tooth and shaping it and hardening it in the patient's mouth sothat hopefully the temporary crown will last until the crown to beformed in the dental laboratory is ready for installation.

Preparing a temporary crown has been a problem in the dental professionfor many years since such temporary crowns frequently break or dislodgebefore the patient returns to the dental office to receive the permanentcrown. Further and of even more significance is that the total procedurepresently employed for crowning a tooth is time consuming on the part ofthe dentist and on the part of the patient since it requires the patientto make two separate visits to the dental office. The current procedurethat requires a dentist to perform all of the dental work in his officewhereas the crown itself is manufactured at a remote location not onlycreates inefficiency but adds to the expense. The primary problem,however, in today's dentistry with the crowning of a tooth is theinconvenience to the patient and the time constraints placed on thedentist. Further, problems with temporary crowns have always been aconcern to dentists.

A method will be described herein in which a dentist can, with a singleoffice visit by a patient, provide the patient a permanent crown.Stating it another way, a basic objective of the invention herein is amethod of preparing a tooth and installing on the prepared tooth apermanent crown that can be done by a dentist entirely within his dentaloffice.

BRIEF SUMMARY OF THE INVENTION

This invention provides a method for making a crown for a patient'stooth in which a dentist can provide a precisely fitted crown of utmostquality during a reasonably short single visit by a patient to thedentist office and without the necessity to resort to the use of adental laboratory or other outside facility.

When a patient requiring a crown appears at the dentist office, thefirst step performed by the dentist is to take an impression of thepatient's teeth, that is, either the upper teeth or lower teethaccording to the location of the tooth requiring the crown. Theimpression is taken in the usual manner as followed by dentists for manyyears in which a soft plastic material having the ability to conform tothe shape of a patient's teeth is placed in a form and pressed againstthe teeth to surround the teeth to the gum level. While the only portionof the impression that will be important is the tooth to be crowned andthe teeth adjacent to it, for all practical purposes, it is easiest forthe dentist to make an impression of the patient's full upper or lowerteeth.

After the impression, a liquid plastic slurry is poured into theimpression and allowed to solidify to provide a model that replicatesthe patient's upper or lower teeth. This model is referred to as a"first model".

If the tooth in its natural state, that is, when the impression is madethat has exterior defects, the dentist applies sculpturing material tofill in such defects and otherwise reshape the tooth on the first moldto that which will be ideal for the external appearance of the crownwhen completed. Material for sculpturing the tooth on the model can thenbe hardened as necessary so that the sculptured tooth presents anexternal shape that is the desired external shape of the crown to becreated.

The dentist then structures the patient's tooth to receive the crown bygrinding away surface portions to provide a tooth base, that is, thepatient's tooth is structurally configured to receive and support acrown. If the crown is to be a full crown, that is to completelysurround the remaining natural tooth then exterior portionssubstantially around the entire tooth are removed so that the crown,when installed, will uniformly circumscribe and cover the entireremaining tooth structure. The grinding away of exterior portions of thetooth to be crowned results in a prepared tooth.

The dentist then makes a second impression of the patient's toothincluding the prepared tooth, and from the second impression, by the useof plaster, a second model is made which replicates the patient's teeth,the second model being differed from the first model in that the toothto be crowned has been changed by the dentist in the process of creatingthe prepared tooth.

The dentist then applies an acrylic releasing plastic foil over thefirst model. In this step plastic foil is heated and air pressureapplied to cause it to conform to the prepared first model to obtain anexternal crown form, that is, a form having a cavity therein thatdefines the external appearance of the crown to be formed. The externalcrown form made by the plastic foil is removed from the first model.

The dentist then places a thin acrylic releasing plastic foil over thesecond model. By "acrylic releasing" is meant a foil that has thecharacteristic that acrylic material used to form a crown does notadhere to it, that is, wherein the formed acrylic that makes the crownis readily releasable from the foil material. The thin acrylic releasingplastic foil is heated and air pressure is applied to it to cause it toconform to and encompass the second model.

The dentist then places moldable crown forming material on the plasticfoil encapsulated prepared tooth on the second model. While the moldablecrown forming material is still in plastic state, the dentist thenplaces the external crown form over the foil covered second mold tocause the moldable crown forming material thereon to simultaneously takean internal contour matching the shape of the prepared tooth and anexternal contour matching the shape of the sculptured tooth. Themoldable crown forming material is then hardened, a step that can beaccomplished very successfully by applying ultraviolet light to themolded crown forming material. The moldable crown forming materialpreferably is a polymer glass ceramic specifically formulated to remainplastic until subjected to high intensity ultraviolet light.

After the ceramic forming material has solidified, the crown can then beremoved from off of the foil covered second mold and out of the externalcrown form. Any surplusage surrounding the crown can be ground away andthe crown polished. The crown is then ready to be cemented in place onthe patient's prepared tooth.

The total procedure can be carried out expeditiously during a one timepatient visit to the dentist office so that the patient, when leavingthe dentist office, will have a permanently mounted crown rather than,with the current procedure, a temporary crown. The steps outlined aboveare not necessary practice in the specific order enumerated.

In the step of placing crown forming material over the foil coveredsecond mold, the dentist may do this in steps, that is, by placing asmall amount of crown forming material on the plastic foil encapsulatedprepared tooth and then hardening the material before placing additionallayers since hardening by the use of ultraviolet light can be mosteffectively accomplished when the crown forming material is not undulythick thereby permitting more effective penetration by the ultravioletlight. The only requirement is that the outer layer of crown formingmaterial must still be in a plastic state when the final external crownform is placed on the second model so that the moldable material willconform to the external crown form.

A better understanding of the invention will be obtained from thefollowing description of the preferred embodiments and claims, taken inconjunction with the attached drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view showing a model that has been made of animpression taken of a patient's lower teeth, the model showing a molarto be crowned. The model is shown positioned in a receptacle that ispart of a machine (not shown) by which heat and pressure is applied to acircular sheet of plastic foil.

FIG. 2 shows the model of FIG. 1 after it has been encapsulated by thesheet of plastic foil. The plastic foil creates an external crown formdefining the exterior configuration of a crown to be manufactured.

FIG. 3 illustrates a second model of the patient's teeth after the toothto receive a crown has been prepared by a dentist. The model is madefrom an impression and is positioned on a platform within a container bywhich heat and pressure is applied to a plastic film to encapsulate themodel.

FIG. 4 shows the second model ready to receive a thin plastic foil bythe application of heat and air pressure.

FIG. 5 shows the second model covered by a thin plastic sheeting that isof the characteristic that ceramic material does not adhere to it.

FIG. 6 shows a portion of the film covered second model.

FIG. 7 shows placing on the prepared tooth of the plastic foilencapsulated second model crown forming material, such as a moldablepolymer glass ceramic.

FIG. 8 is an exploded view showing the film encapsulated second modelhaving ceramic forming plastic material thereon as shown in FIG. 7 andshows the external crown form obtained in FIG. 2 to be placed down overthe film covered second model.

FIG. 9 shows the form obtained in FIG. 2 pressed down over the filmcovered second mold to cause the plastic ceramic forming material toconform to both the interior and exterior configuration of the desiredcrown and shows the application of ultraviolet light to solidify thecrown forming material.

FIG. 10 is an exploded view showing the form removed from the foiledcovered second model and shows the crown having been formed as a resultof the solidification or curing of the crown forming material.

FIG. 11 shows the created crown being removed from the film coveredsecond model. The crown is ready to have any surplusage ground away fromit and then polished so that it is in condition to be cemented onto theprepared tooth of the patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When a patient comes to a dentist requiring a tooth to be crowned, thedentist first obtains an impression of either the upper teeth or lowerteeth that contains the tooth to be crowned. This step is notillustrated in the drawings since it is a step that has long beenpracticed by dentists and is a familiar procedure to any person who hashad a crown, bridge or other restorative dentistry. The impression isformed by placing a soft pliable material into a holder shaped toaccommodate the upper or lower teeth of a patient. After the holderhaving the impression material therein is pressed around the teeth, itis removed and a slurry of model forming material, such as plaster, ispoured into the impression. Plaster is the most commonly used materialin dentistry for forming a model. Plaster is desirable because of itsconvenience, economy and the fact that it sets up rapidly. This stepresults in providing a model of the patient's teeth which includes theteeth to be crowned hereinafter referred to as a first model.

FIG. 1 shows a first model, generally indicated by the numeral 10, of apatient's teeth. Model 10 is, as previously indicated, typically ofsolidified plaster and includes a tooth 12, a molar in this case, thatrequires a crown. The model includes some of the gum portion 14 of thepatient's tooth supporting structure.

In creating a crown it is normally desirable that the finished crownwill have a shape substantially that of the normal tooth before thetooth is prepared to receive the crown. It is normally desirable in theformation of a crown to be placed on a prepared tooth for the crown tohave a configuration substantially similar to the normal tooth of thepatient before the dentist has done preparatory work on the tooth.However, many teeth and particularly ones requiring crowns may havedefects in their exterior appearance, such as teeth having portions thathave been broken away or have deteriorated. For this reason, after model10 has been made from an impression the dentist may apply moldingmaterial to tooth 12 to reconfigure and shape it to eliminateimperfections and to create a model in which the tooth has the externalappearance of the crown to be created. Tooth 12 of first model 10 asshown in FIG. 1 has been sculptured as required by the dentist so thatit appears substantially identical to the desired external appearance ofthe finished crown.

The next step illustrated in the drawing, as indicated by FIG. 1, is toobtain a form replicating model 10. This can be accomplished utilizingreadily commercially available equipment, such as manufactured byScheu-Dental of Iserlohn, Germany and sold under the trademark"BIOSTAR". This equipment includes a platform (not seen in FIG. 1 butshown in FIG. 3) on which first model 10 rests in a container positionedwithin a housing that support structure by which a plastic foil isheated and subjected to air pressure to cause the plastic foil to formaround first model 10 as seen in FIG. 2. FIG. 2 shows the plastic foil18 having been heated and forced by air pressure to closely adhere tothe external configuration of the first model 10 to provide a plasticform indicated by the numeral 20, the plastic form 20 being the plasticfoil 18 after it has been heated and conformed by air pressure to theexternal shape of the patient's teeth including the tooth to receive thecrown.

Plastic foil 18 is available from Scheu-Dental and is sold under thetrademark "COPYPLAST". It is a tough plastic clear foil that does notbond to acrylic or ceramic forming molding compositions as employedherein. Plastic foil 18 is heated by use of ultraviolet light to atemperature of typically about 420° F., which requires typically aboutone minute, after which air pressure is applied above the heated film toforce it down over and around the teeth replicated in first model 10,requiring only a few seconds.

After the plastic foil 18 has cooled, taking only a minute or so, theair pressure can be released and the plastic foil covered first modelremoved from the machine. The foil form 20 is easily removed from themodel and is used in making a crown as will be explained subsequently.Therefore, in FIG. 2 the finished form 20 has the external shape of thedesired external configuration of a finished crown.

Next the dentist then shapes the patient's natural tooth to be crownedin a way to provide a prepared tooth, that is a tooth that isconditioned to receive a crown. This is accomplished by removingexterior portions of the tooth. Exterior portions of the natural toothmust be removed sufficient so that the crown will have thickness to giveit strength while, at the same time, the prepared tooth must have asmuch of the natural tooth remaining as is necessary to providestructural support for the crown.

After the dentist has prepared the natural tooth to receive a crown, asecond impression is made, not shown in the drawings, and from thesecond impression, a second model is made, such as of plaster, thesecond model being indicated by the numeral 22 in FIG. 3. The secondmodel shows the configuration of the tooth to receive the crown, themodel of the prepared tooth being indicated by the numeral 12A. Secondmodel 22 is shown in FIG. 3 as it is placed on a platform 24 of formmaking apparatus 16. FIG. 4 shows second model 22 positioned within theform making apparatus 16. To fill up space around the model so that theresulting form more successfully contours the model the empty space isfilled with a granular material 26 as seen in FIG. 4 and also in FIG. 1.The granular material is commonly used in the equipment for makingplastic forms but is not directly involved in the invention.

FIG. 4 shows the placement of a disk of thin, plastic foil 28 over thesecond model 22 which, by the application of heat and air pressure isforced to closely conform to the exterior of the second model asillustrated in FIG. 5. Plastic foil 28 is commercially available fromScheu-Dental and sold under the trademark "ISOFOLAN". It does not bondto acrylic or to ceramic forming molding compositions used herein.

The steps as illustrated in FIG. 4 and 5 result in encapsulating theteeth of second model 22 with a thin ceramic releasing film. The filmencapsulated model is indicated by the numeral 30 in which the model ofthe prepared tooth 12A is encapsulated by film 28.

While the procedures of treating first model 10 in FIGS. 1 and 2 andthat of treating second model 22 in FIGS. 3 and 4 are essentially thesame, they are carried out for entirely different purposes. FIGS. 1 and2 illustrate the procedure for creating a form 22 that will be usedlater in the process, the form being used to define the exteriorconfiguration of the crown. The processes of FIGS. 3 and 4 is to providea foil covering over second model 22 and particularly over tooth 12A tobe crowned. The reason that the plastic covering is required asillustrated in FIGS. 3 and 4 is to achieve a surface over the model ofthe tooth to be crowned to which ceramic forming material does notadhere.

After the plastic film covering has been applied to the second model asillustrated in FIG. 3, the dentist is ready to form the crown that willbe used to apply to the patient's prepared tooth. A summary of importantsteps in the sequence of steps for making a crown is illustrated inFIGS. 6 through 11. FIG. 6 shows a broken away portion of model 22 withplastic foil 28 thereon. FIG. 6 is essentially the second model 22 asshown in FIG. 5 with the thin plastic foil securely conformed to it toprovide the film encapsulated model 30. However, FIG. 6 shows only afragmentary portion of second model 22. In practicing the invention, thefirst and second models 10 and 22 are best maintained as initiallyformed, that is, where the model typically includes the entire upper orlower teeth of the patient, however, FIGS. 6 through 11 show onlyfragmentary portions of second model 22 to simplify the illustrations.While the first and second models are typically maintained in tact, theplastic foil after having been conformed to the shape of the models maybe trimmed away to include only the portion encompassing the tooth to becrowned and the teeth adjacent to it. Trimmed away portions of theplastic foil forms are shown in FIGS. 6 through 11.

As previously indicated, FIG. 6 shows second model 22 having the tooth12A sculptured in the shape to receive a crown and the tooth, includingthe teeth adjacent to it, encapsulated in a plastic foil 28 for the solepurpose of providing a surface to which ceramic forming material willnot adhere. The plastic foil 28 encapsulating second model 22 asillustrated in FIG. 6 is not employed to change the shape of the crownto be formed and therefore the film is as thin as possible. If thesecond model could be manufactured of a material to which ceramicmaterial does not adhere, then the use of plastic foil 28 would not berequired, however, no such practical model making material is known atthis time.

FIG. 7 shows the foil encapsulated crown as seen in FIG. 6 but withmoldable ceramic forming material 32 applied to the foil coveredprepared tooth 12A. Ceramic forming material 32 is preferably apolymer-glass moldable ceramic that is commercially available in aplastic state and that can be hardened to a ceramic solid by theapplication of ultraviolet light. The ceramic forming material 32 ismanually placed on prepared tooth 12A in sufficient quantity to form therequired crown.

FIG. 8 shows the step of inserting a trimmed away section of form 20obtained in the process illustrated in FIGS. 1 and 2, that is, the form20 is cut away from the plastic foil 18 after it has been conformed byheat and pressure to the exterior of the first model that includes asculptured configuration of tooth 12 having a form of the exteriorconfiguration of the crown. Thus, the form 20 has the desired exteriorconfiguration of the crown whereas the foil encapsulated model 30provides the interior or concave configuration of the crown. When form20 is pressed down over the film encapsulated model 30, ceramic formingmaterial 32 takes an exterior shape defined by form 20 and an interiorshape defined by foil encapsulated model 30.

FIG. 9 shows form 22 pressed down over foil encapsulated model 30 topress the ceramic forming material 32 into the desired shape of thecrown. An ultraviolet light source 34 is then placed adjacent to ceramicforming material 32 surround the prepared tooth to solidify it.

After the ceramic forming material has solidified, form 20 is removedfrom the film encapsulated model 30 as illustrated in FIG. 10, leavingthe hardened crown 36 which, as illustrated in FIG. 11, can be removedfrom film encapsulated model 30. Thus, the crown 36 has been completed.If, when form 20 is removed from film encapsulated model 30 crown 36remains within the confines of form 20 the form can be cut away, beingno longer required, to extract the crown. In any event, the crown 36 isremoved as a separate, created element which the dentist can then finishfor use for cementing onto the patient's prepared natural tooth. Crown36 as formed by this process may require the removal of extraneousceramic forming material which can be done by grinding away anysurplusage. The crown 36 can be polished and subjected to finalhardening processes, such as by subjecting the crown to more intense andprolonged exposure to ultraviolet light as necessary to insure that thecrown forming material has reached its desired degree of hardness.

Crown 36 is then ready for cementing into position on the patient'sprepared tooth 12A in exactly the same way as a crown having beenproduced by a laboratory. However, the entire procedure as describedherein can be consummated within a dentist office. The procedure thuseliminates the necessity for applying a temporary crown to the patient'sprepared tooth while a permanent tooth is being prepared. Further, manyof the steps in the procedure can be done by dental technicians in thedentist office. The trained skill of the professional dentist isparticularly required for structuring for the tooth to receive a crown,for applying sculpturing material to the tooth to be crowned asreplicated in the first mold, the final shaping and polishing of thefinished crown 36 and cementing the crown onto the patient's preparedtooth. Many of the other steps can be accomplished by a trainedassistant.

The steps illustrated and described herein are the essential steps andin the actual practice of the procedures secondary steps may be employedto facilitate formation of a superior crown. For instance, FIGS. 7 and 8show the deposition of ceramic forming material 32 onto the film coveredprepared tooth 12A, followed by positioning form 20 down over the filmencapsulated model to force the plastic ceramic forming material to takethe desired shape followed by the application of ultraviolet light asshown in FIG. 9. In actual practice, it may be necessary to place layersof the ceramic forming material 32 onto the film covered prepared tooth12A and hardened the inner layers using ultraviolet light with only thefinal outside layer of the ceramic forming material 32 being on thetooth 12A when form 20 is applied over it so that the desired externalshape of the crown is obtained. The reason for placement of the ceramicforming material in layers is that this material hardens mosteffectively when it is of a relatively shallow depth since ultravioletlight loses intensity when it penetrates the material and therefore theceramic forming material can be more successfully hardened when done instages.

The claims and the specification describe the invention presented andthe terms that are employed in the claims draw their meaning from theuse of such terms in the specification. The same terms employed in theprior art may be broader in meaning than specifically employed herein.Whenever there is a question between the broader definition of suchterms used in the prior art and the more specific use of the termsherein, the more specific meaning is meant.

While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of construction and the arrangement of components withoutdeparting from the spirit and scope of this disclosure. It is understoodthat the invention is not limited to the embodiments set forth hereinfor purposes of exemplification, but is to be limited only by the scopeof the attached claim or claims, including the full range of equivalencyto which each element thereof is entitled.

What is claimed:
 1. A method of making a crown for a patient's toothcomprising the steps of(1) making an impression of the patient's teethincluding at least the portion thereof including the tooth to becrowned; (2) by use of the impression obtained in step (1) making afirst model, that replicates the patient's teeth including at least theportion thereof having the tooth to be crowned; (3) applying sculpturingmaterial to the tooth to be crowned as replicated in said first modelobtained in step (2) to obtain a prepared first model having asculptured tooth with the desired appearance of the crown; (4) placingan acrylic releasing plastic foil over said prepared first modelobtained in step (3); (5) heating and pressuring said plastic foil tocause it to conform to said prepared first model to obtain an externalcrown form; (6) removing said external crown form from said preparedfirst model; (7) treating the tooth to receive a crown by removal ofsurface portions to provide a prepared tooth; (8) making an impressionof the patient's teeth including at least the portion thereof includingsaid prepared tooth; (9) by use of the impression obtained in step (8),making a second model, that replicates the patient's teeth including atleast the portion thereof having said prepared tooth; (10) placing athin acrylic releasing plastic foil over said second model as obtainedin step (9); (11) heating and pressuring said thin acrylic releasingplastic foil to cause it to conform to and encompass said prepared toothas replicated in said second model; (12) placing moldable crown formingmaterial on the plastic foil encapsulated prepared tooth on said secondmodel; (13) placing the external crown form obtained in steps (5) and(6) over said foil covered second mold to cause said moldable crownforming material thereon to take an internal contour matching the shapeof said prepared tooth and an external contour matching the shape ofsaid sculptured tooth obtained in step (3); (14) hardening the moldablecrown forming material to cause the creation of a crown; (15) removingthe crown from off of said foil covered second model and out of saidexternal crown form; and (16) removing any surplusage from the crownobtained from step (15) and polishing the crown to provide a preparedcrown ready to be cemented onto said patient's prepared tooth.
 2. Amethod of making a crown for a tooth according to claim 1 wherein step(14) is carried out employing ultraviolet light.
 3. A method of making acrown for a tooth according to claim 1 wherein said moldable crownforming material employed in step (12) is a polymer glass ceramic.
 4. Amethod of making a crown for a tooth according to claim 1 wherein step(12) is carried out in more than one stage by first placing a layer ofmoldable crown forming material on said plastic foil encapsulatedprepared tooth of said second mold, hardening the layer followed by theapplication of an additional layer or layers, the final layer remainingin a plastic state to receive step (13) whereby the external contour ofthe crown forming material will match the shape of the sculptured toothobtained in step (3).